There have been known automotive vehicles of a type constructed in such a manner that, if given control is necessary even while an ignition switch is kept OFF in order to prevent discharge of a vehicle-mounted power supply, a control device for performing the given control is caused to shift to a so-called “sleep” state. When there arises a need for the control device to perform the given control while the control device is in the sleep state, a signal is supplied to a wake-up signal input terminal of the control device to place the control device in a wake-up or normal operating state.
In electronically-controlled vehicle seatbelt apparatus, once the seatbelt is detached from the body of a vehicle occupant while the control device is in the sleep state with the ignition switch kept in the OFF state, there arises a need to activate a motor to automatically take up the seatbelt into a predetermined storage position. Thus, the seatbelt apparatus are constructed so that, even while the control device is in the sleep state, electric power continues to be supplied to a buckle switch and its related detection section for detecting an attached (i.e., worn)/non-attached (i.e., non-worn) state of the seatbelt in such a manner that a detection signal indicative of an ON/OFF state of the buckle switch is supplied to the wake-up signal input terminal of the control device.
In connection with the seatbelt apparatus constructed in the aforementioned manner, Japanese Patent Application Laid-Open Publication No. 2006-175896 discloses a vehicle occupant protection apparatus that employs a technique for reducing electric power to be supplied to the detection section of the buckle switch. In connection with the buckle switch for detecting the attached/non-attached state of the seatbelt, the disclosed vehicle occupant protection apparatus includes a first detection circuit having a first switch that is opened when the seatbelt is worn or attached around the body of a vehicle occupant and closed when the seatbelt is not attached, and a second detection circuit having a second switch that is closed when the seatbelt is attached around the body of the vehicle occupant and opened when the seatbelt is not attached. The control device in the form of an ECU supplies electric power to the first or second detection circuit of which the switch is in the opened state. Further, operation of a driving motor is controlled by the control device on the basis of a detection signal output from the first or second detection circuit currently supplied with electric power. When the control device (ECU) is in the sleep state, the sleep state is canceled once a change occurs in the detection signal output from the first or second detection circuit. Further, the disclosed apparatus is constructed to stop the electric power supply to each of the first or second detection circuits when the switch in the circuit is in the closed state, to thereby reduce the electric power supply.
Reducing the electric power to be supplied to the detection section of the buckle switch in the vehicle seatbelt apparatus is an important technique from the viewpoint of reduction in power consumption of a battery, but the conventionally-known technique does not consider at all how the seatbelt should be controlled in accordance with the current state of the buckle switch when the control device has woken up. Thus, when the seatbelt was paid out while the control device was in the sleep state, there would occur a situation against the wish of the vehicle applicant seated in the seat, so that comfortable attachment of the seatbelt is unattainable.